The invention relates to packaging electrical components for converters and power magnetics.
One approach to packaging electric components in power converters (FIG. 1) includes providing a structure 1 having a housing which encloses both the components and the means by which heat is extracted from the components. The housing includes a non-conductive casing 5 and an aluminum heat-sinking base. A printed circuit board (PCB) 3 is mounted next to the upper wall 5a of the casing. Conductive pins 7 are attached directly to the PCB 3 and extend up through the wall 5a. Electronic components 9a, 9c are mounted to one or both sides of the PCB 3. Larger size components such as the transformer 9c are mounted to the lower side where space is available. Power-dissipating devices such as 9b are mounted directly on the base-plate 6 for better heat transfer. Power components 9b are electrically connected to the PCB by leads 12. Some of the power-dissipating devices 9d are attached to the base-plate by means of a thermally conductive insulator material 8. Structure 1 may be filled with an encapsulant, which acts as a heat spreader and provides mechanical support. In the case where a hard epoxy encapsulant is used, a xe2x80x9cbuffer coatingxe2x80x9d material is used to protect some of the components.
However, there is a need for improved transformers.
The present invention provides for many improvements in the field of transformer layout and construction.
In one embodiment of the invention, a new packaging technology which improves the electrical and mechanical performance of circuits using magnetic elements is provided. In this embodiment, high frequency current loops generate electromagnetic fields, which are radiated, or induce high frequency current in the rest of the circuit. To reduce the radiated field, the extent of these loops is minimized by locating the high frequency switching components close to each other and very close to the magnetic elements. By separating the high frequency switching electronic components from the rest of the electronic components and locating them on the same multilayer PCB where the magnetic element is located, optimal results are obtained.
The invention provides a packaging technology for power converters and power magnetics that is compact, inexpensive, and easy to manufacture. The invention features a package for electrical components on a circuit board. In this packaging concept most of the power magnetic elements are integral to the multilayer PCB. The windings of the magnetic elements such as transformers, inductors, and in some cases signal transformers are incorporated in the multilayer PCB, with the top and bottom layers providing support for electronic components. In this way the footprint of the magnetic elements is reduced to the footprint of the transformer core. The power-dissipating devices are placed on pads, which have a multitude of copper plated vias to the other side of the PCB. The heat transferred to the other side of the PCB can be further spread using a larger pad, or transferred to a metallic base-plate attached to the PCB through an isolating material. Due to the limited surface of the heat spreader, an additional heat sink may be attached to the heat spreader to increase its cooling area.
The unique aspect of this packaging concept is the fact that the magnetic element""s windings are incorporated on the multilayer PCB construction which also serves as a support for power-dissipating components and some of the control components. The heat from the power-dissipating components is extracted through copper plated vias which transfer the heat to the other side of the PCB. The heat is further transferred to a metal base-plate connected to the PCB by means of a thermally conductive insulator. For airflow cooling applications the heat spreader connected to the thermal vias can serve as a cooling surface. A heatsink can also be attached to the heat spreader to increased the heat dissipation area.
The new packaging technology of this invention improves the electrical and mechanical performance of circuits which include magnetic elements.
Switched mode power processing converters employ high frequency currents. High frequency current loops are created by high frequency switching electronic components and the interconnection paths between them.
The high frequency current loops generate electromagnetic fields, which are radiated and induce high frequency current in the rest of the circuit. To reduce the radiated field these loops should be as small as possible. As a result the high frequency switching components are located close to each other and very close to the magnetic elements. This is achieved more particularly by separating the high frequency switching electronic components from the rest of the electronic components and locating the high frequency switching electronic components on the same multilayer PCB carrying the magnetic elements. The multilayer PCB which incorporates the winding of the magnetic element contains more layers than most of the multilayer PCBs which serve as support and interconnection between electronic components.
To reduce the cost of the assembly it is desirable to reduce the cost of the multilayer PCB that incorporates the magnetic elements. This multilayer PCB that contains the magnetic element and the high frequency switching electronic components is herein referred to as the power PCB. The multilayer PCB that accommodates the rest of the electronic components is referred to as the mother PCB. The high frequency switching electronic components are located on the power PCB close to each other and close to the magnetic element. As a result the size of the high frequency current loop can be significantly reduced. The interconnection between the power PCB and the mother PCB will carry lower frequency currents. This package concept leads to better electrical performance while providing an economical utilization of expensive multilayer PCBs.
According to the invention, the electronic components are located very close to the magnetic elements in order to minimize the size of current loops through the magnetic elements.
The invention, together with various embodiments thereof, will be more fully explained by the accompanying drawings and the following descriptions thereof.